Some well-known conventional heat exchangers of this type are cross flow type heat exchangers using a corrugation process (see, for example, Patent Document 1 below).
Referring to the schematic perspective view of FIG. 8, a conventional heat exchanger 104 will be described.
As shown in FIG. 8, heat exchanger 104 includes a plurality of heat exchanger blocks 101 each having a heat exchanger plate 102 and a corrugated spacer plate 103 bonded thereto. The heat exchanger plate 102 is made of paper treated with a hydrophilic polymer containing a moisture absorbent such as lithium chloride. The heat exchanger blocks 101 are stacked over each other while being rotated by 90 degrees each time.
In heat exchanger 104 thus structured, a first airflow “A” and a second airflow “B” are made to pass through the spaces between heat exchanger plates 102 and spacer plates 103 in the directions of the arrows of FIG. 8. As a result, the first and second airflows “A” and “B” exchange heat through heat exchanger plates 102.
Another conventional heat exchanger of this type has moisture permeability, a gas shielding property, and a flame retardant property (see, for example, Patent Document 2 below).
The heat exchanger having moisture permeability, gas shielding property, and flame retardant property is described as follows. This heat exchanger is described with reference to FIG. 8 because it has an external shape similar to the conventional heat exchanger described above.
Heat exchanger plates 102 having moisture permeability, gas shielding property, and flame retardant property are formed as follows. First, a mixed solution is prepared by adding a guanidine salt-based flame retardant agent and an organic or inorganic moisture absorbent to an aqueous solution of a water-soluble polymeric resin. Then, the mixed solution is either impregnated or coated in flammable porous members such as Japanese paper therewith to form heat exchanger plates 102. The heat exchanger 104 including such heat exchanger plates 102 has high latent heat exchange efficiency, low migration of gas such as carbon dioxide, and an excellent flame retardant property.
The high latent heat exchange efficiency of the heat exchanger 104 is achieved due to the following reasons. The flammable porous members such as Japanese paper made of hydrophilic fibers used as the substrates of heat exchanger plates 102 allow water molecules to be absorbed and dispersed therein at high speed. In addition, the organic or inorganic moisture absorbent improves the moisture permeability of the porous members. The low migration of gas such as carbon dioxide of heat exchanger 104 is achieved by impregnating or coating the porous members with the water-soluble polymeric resin such as a polyvinyl alcohol resin, making the porous members less breathable. The excellent flame retardant property is achieved by impregnating or coating the porous members with the guanidine salt-based flame retardant agent.
Another conventional heat exchanger of this type has moisture-resistant heat exchanger plates which allow the heat exchanger to be used in an environment susceptible to dew condensation such as a cold region, a bathroom, or a heated swimming pool (see, for example, Patent Document 3 below).
The heat exchanger having moisture-resistant heat exchanger plates 108 is described as follows with reference to FIG. 9. FIG. 9 is a schematic sectional view of one of heat exchanger plates 108. This heat exchanger is described with reference to FIG. 8 because it also has an external shape similar to the heat exchanger of FIG. 8.
As shown in FIG. 9, each heat exchanger plate 108 of heat exchanger 104 consists of porous substrate 109 such as an unwoven cloth having a specific air permeability, and a moisture permeable film formed by coating water-insoluble hydrophilic polymer 110 thereon.
The moisture resistance of the heat exchanger plates 108 is achieved by using an unwoven cloth as the porous substrate 109 and also using the water-vapor permeable film as the water-insoluble hydrophilic polymer 110. This allows the heat exchanger 104 to have less shape distortion in an environment repeatedly subjected to dew condensation.
Another conventional heat exchanger of this type has heat exchanger plates each made of a composite moisture permeable film in order to resist deformation, maintain performance for a long time, and has high latent heat exchange efficiency in an environment susceptible to dew condensation (see, for example, Patent Document 4).
The heat exchanger having the heat exchanger plates each made of the composite moisture permeable film is described as follows with reference to FIG. 10. FIG. 10 is a schematic sectional view of one of the heat exchanger plates 116. This heat exchanger is described with reference to FIG. 8 because it also has an external shape similar to the heat exchanger of FIG. 8.
As shown in FIG. 10, each heat exchanger plate 116 is a composite moisture permeable film consisting of a fibrous porous sheet 112, a hydrophilic polymer thin film 113, and a porous film 114 disposed therebetween. The fibrous porous sheet 112 is water-insoluble and highly breathable. The hydrophilic polymer thin film 113 is water-insoluble and water-vapor permeable. The porous film 114 is water-insoluble and has smaller diameter pores than the fibrous porous sheet 112. The heat exchanger 104 is formed as follows. First, each heat exchanger block 101 is formed by bonding the spacer plate 103 and heat exchanger plate 116 together by applying an adhesive (unillustrated) to the peaks on one side of corrugated spacer plate 103. Then, the peaks on the other side of corrugated spacer plate 103 on the heat exchanger block 101 are applied with the adhesive (unillustrated). Finally, heat exchanger blocks 101 are stacked on each other while being rotated by 90 degrees each time.
In each heat exchanger plate 116 of conventional heat exchanger 104, the water-insoluble hydrophilic polymer thin film 113, which is moisture permeable and the main contributor to gas shielding, is formed on the highly breathable fibrous porous sheet 112 with the porous film 114 interposed therebetween. This structure allows hydrophilic polymer thin film 113 to be sufficiently thin, and at the same time, to avoid pinholes or peeling. As a result, the heat exchanger 104 has a low gas migration rate and a high latent heat exchange efficiency. In addition, heat exchanger plates 116 made of the water-insoluble materials allow the heat exchanger 104 to resist deformation and maintain performance for a long time in an environment susceptible to dew condensation.
Another conventional heat exchanger of this type has heat exchanger plates each made of a composite film and spacer plates each made of a composite film in order to improve the mass production and the basic performance of the heat exchangers in addition to the above-described performance (see, for example, Patent Document 5 below).
The heat exchanger having heat exchanger blocks 127 is described as follows with reference to FIG. 11. Each of the heat exchanger blocks 127 has a heat exchanger plate and a spacer plate which are each made of a composite film. FIG. 11 is a schematic sectional view of one of heat exchanger blocks 127. This heat exchanger is described with reference to FIG. 8 because it also has an external shape similar to the heat exchanger of FIG. 8.
As shown in FIG. 11, each spacer plate 120 is formed by joining a thin film 121 having an air shielding property to a porous material 122, and then joining the thin film 121 to an adhesive layer 123 exhibiting adhesion when softened by heat. In this specification, “to join films” means “to bring films into close structural contact with each other” by being superimposed upon each other, bonded to each other, or subjected to a process such as heat sealing or lamination.
Each heat exchanger plate 124, on the other hand, is formed by joining hydrophilic polymer thin film 125 to porous material 122, and then joining thereto ground fabric 126. Hydrophilic polymer thin film 125 is water-insoluble and water-vapor permeable. Ground fabric 126 is breathable and thicker than the combined thickness of porous material 122 and hydrophilic polymer thin film 125. The heat exchanger 104 of Patent Document 5 is formed as follows. First, each heat exchanger block 127 is formed by bonding spacer plate 120 and heat exchanger plate 124 together with adhesive layer 123. Then, the corrugated peaks of heat exchanger blocks 127 are applied with an adhesive (unillustrated). Finally, heat exchanger blocks 127 are stacked over each other while being rotated by 90 degrees each time.
The bonding between spacer plates 120 and heat exchanger plates 124 is performed by using adhesive layer 123 which exhibits adhesion when softened by heat. This provides heat exchanger 104 with, in addition to the above-described performance, the advantage of being manufactured by heat sealing which has fast initial bonding strength. As a result, heat exchanger blocks 127 can be bonded quickly and continuously. In the process of bonding the heat exchanger blocks 127 by applying the adhesive (unillustrated) to the peaks of the corrugated spacer plates 120, the adhesive easily enters porous materials 122 of the spacer plates 120 and provides an anchor effect. When the heat exchanger 104 is in use, the anchor effect increases the bonding strength between the heat exchanger blocks 127, making the spacer plates 120 and heat exchanger plates 124 harder to be separated from each other. In addition, the thin films 121 having air shielding property of spacer plates 120 prevent gas migration, that is, air leakage to the outside. The porous materials 122 are easy to cut and the heat exchanger blocks 127 are firmly bonded to each other. Accordingly, these features facilitate cutting the heat exchanger 104, where heat exchanger blocks 127 are stacked, and the manufactured heat exchanger 104 has a desired size.
Conventional heat exchanger 104 having moisture permeability, gas shielding property, and a flame retardant property, however, has the following drawbacks. Heat exchanger plates 102 are formed by impregnating or coating the flammable porous members such as Japanese paper with the mixed solution prepared by adding the guanidine salt-based flame retardant agent and the organic or inorganic moisture absorbent to the aqueous solution of the water-soluble polymeric resin. In an environment repeatedly subjected to dew condensation, however, the water-soluble polymeric resin impregnated or coated in the porous members therewith gradually elutes in water because of its water solubility, thereby deteriorating the gas shielding property. Moreover, the guanidine salt-based flame retardant agent and the organic or inorganic moisture absorbent also gradually elute in water from the porous members, thereby deteriorating the moisture permeability and the flame retardant property. Therefore, there is a need for a heat exchanger which, in an environment repeatedly subjected to dew condensation, prevents deterioration due to dew condensation water, retains the components of the heat exchanger plates, and maintains basic performance such as moisture permeability, gas shielding property, and a flame retardant property.
On the other hand, conventional heat exchanger 104 having moisture-resistant heat exchanger plates 108 has the following drawbacks. Heat exchanger plates 108 each consist of porous substrate 109 such as an unwoven cloth having high air permeability and the moisture permeable film formed thereon by coating water-insoluble hydrophilic polymer 110. This structure requires water-insoluble hydrophilic polymer 110 to be thick, causing a reduction in the moisture permeability and hence the latent heat exchange efficiency. In contrast, if hydrophilic polymer 110 is thinner, this reduces the bonding strength between porous substrate 109 and the moisture permeable film of water-insoluble hydrophilic polymer 110. As a result, the moisture permeable film becomes susceptible to peeling, pinholes, and airflow leakage, thereby degrading the basic performance of the heat exchanger. Therefore, there is a need for a heat exchanger which, in an environment repeatedly subjected to dew condensation, prevents deterioration due to dew condensation water, prevents peeling of the heat exchanger plates, and maintains basic performance such as airflow leakage prevention. In conventional heat exchangers, the corrugated thickness of spacer plates 103 and 120 causes the airflow passages in heat exchanger plates 102, 108, 116, and 124 to have a small effective area and hence high ventilation resistance. Therefore, there is a need for a heat exchanger which has low ventilation resistance.
Conventional heat exchanger 104 having heat exchanger plates 116 each made of the composite moisture permeable film has the following drawbacks. Heat exchanger blocks 101 each consist of heat exchanger plate 116 and corrugated spacer plate 103 whose peaks are applied with the adhesive so as to be bonded to heat exchanger plate 116. This structure makes spacer plates 103 have a large contact area with heat exchanger plates 116, so that the adhesive applied to spacer plates 103 causes heat exchanger plates 116 to have a smaller effective area for water vapor permeation. The effective area for water vapor permeation in heat exchanger plates 116 is further reduced by the adhesive applied to the corrugated peaks of heat exchanger blocks 101 to stack them on top of each other so as to form heat exchanger 104. This causes a reduction in the latent heat exchange efficiency. Therefore, there is a need for a heat exchanger having high latent heat exchange efficiency.
Conventional heat exchanger 104 having heat exchanger plates 124 each made of a composite film and spacer plates 120 each made of a composite film has the following drawbacks. The bonding between spacer plates 120 and heat exchanger plates 124 is performed by using adhesive layer 123 which exhibits adhesion when softened by heat. This allows heat exchanger 104 to be manufactured by heat sealing which has fast initial bond strength. In heat exchanger blocks 127, only the peaks of spacer plates 120 are bonded to heat exchanger plates 124. As a result, the effective area for water-vapor permeation is less reduced than in heat exchanger 104 having heat exchanger blocks 101 in which only heat exchanger plates 116 are each made of the composite moisture permeable film. However, the bonding between heat exchanger blocks 127 is performed by applying the water-soluble adhesive to the peaks of corrugated spacer plates 120. The water-soluble adhesive, which is slow to cure and highly fluid, seeps to the heat transfer surfaces of heat exchanger plates 124 from the upper peaks of spacer plates 120. This reduces the effective area for water vapor permeation in heat exchanger plates 124, and hence the latent heat exchange efficiency. Therefore, there is a need for a heat exchanger having high latent heat exchange efficiency.
Patent Document 1: Japanese Patent Examined Publication No. S47-19990
Patent Document 2: Japanese Patent Examined Publication No. S53-34663
Patent Document 3: Japanese Patent No. 1793191
Patent Document 4: Japanese Patent No. 2639303
Patent Document 5: Japanese Patent No. 3460358